Chromium plating



nited States Patent 'ice CHROMIUM PLATING Frank Passal, Detroit, Mich.,assignor to Metal & Thermit Corporation, Woodbridge Township, N.J., acorporation of New Jersey No Drawing. Filed Nov. 22, 1957, Ser. No.698,062

15 Claims. (Cl. 20451) ing spray and mist, it is necessary to designspecial equipment and to provide large ventilation capacity. Thiscorrosive spray and mist is caused by the formation of gas bubbles atthe electrodes (oxygen at the anodes and hydrogen at the cathodes).These bubbles are relatively large and when they break at the surface,the electrolyte spatters into very fine droplets which become airborne.

Certain additives having strong wetting characteristics. are, and havebeen, used to reduce mist and spray. How-- ever, none of the additivesnow known are completely successful from a commercial viewpoint. Someare useful for very short periods of time but then rapidly decompose inthe highly oxidizing chromic acid baths. Others, although effective inpreventing spray and mist, are strongly adsorbed on the cathodesresulting in electrodeposits that have poor adhesion and that arepitted.

The most successful additives are the fiuorinated long chainhydrocarbons which are very expensive. I

It is an objective of this invention to provide a process forelectroplating chromium from chromic acid baths with concomitantproduction of a minimum of spray and mist.

It is another object of this invention to provide a composition ofmatter which when incorporated in chromic acid baths minimizes theproduction of spray and mist during electrodeposition.

The invention also contemplates the use of chromic acid baths from whichchromium may be electrode posited with a minimum of mist and spray atthe surface.

I have now discovered that when chromium is electrodeposited from achromic acid bath in which is incorporated a small but effective amountof a sulfonated alkyl diphenyl oxide, the electrodeposition is carriedout,

wherein R is an alkyl group having from 6 to 18 carbon atoms in thechain and X is a catio'maiid it has-a value 'of octadecyl groups.

phenyl oxide and didodecyl diphenyl oxide.

0 or 1. The cation, X, is selected from hydrogen, ammonium and metals,and excludes metalloids which are converted in the chromic acid bath toacid radical anions which have a deleterious effect on the bath or onthe electrodeposited chromium.

barium, magnesium, nickel, iron, and copper. The preferred compounds arethe sulfonated salts of sodium,

potassium, lithium or ammonium. The operative alkyl.

groups, R, includes the hexyl, octyl, nonyl, dodecyl and The octyl,nonyl and dodecyl groups are preferred. Chromic acid baths are highlyacid .and

strongly ionizing in nature. The sulfonated alkyl diphenyl oxide in thebath is believed to exist in the formv of the acid radical, having theformula:

Ru 1. B

so.- o:-

' The sulfonated alkyldipenhyl oxide as produced and utilized is amixture of. the various substituted products. The sulfonic acidsalt'group is believed primarily substituted in the position ortho tothe oxygen-substituted carbon, whereas the alkyl chain is primarilysubstituted in the para position. The additive as commercially pro'duced and utilized may also be a mixture of monoand dialkyl substitutedproducts.- A preferred additive is a mixture of the disulfonated saltsof monododecyl dium and dipotassium salts are preferred.

' bath.

It have discovered that when as little as 0.005 g./l. (gram per liter)of sulfonated alkyl diphenyl oxide is added to a chromic acid bath inthe chromium plating. process, the'amount of mist and spray is verysubstan-" tially reduced. Although these additives are stable in chromicacid baths, they do decompose to a slight extent and over a period oftime are used up," to which drag-out contributes. The minimum initialamount added to the bath is to a large extent governed by thecontemplated replenishment rate. It is also in part governed by costconsiderations and by the actual construction of the plating tanks.Baths containing this additive have a stable foam blanket on thesurface. It is desirable that this blanket should be stable and ofsubstantial, yet not too great, thickness, which could be dangerousbecause of the large amount of entrapped oxygen and hydrogen. For thisreason the geometry of the plating system affects the desiredconcentration of additive as it will aifect the thickness of the foamblanket for a given volume of It is not contemplated that more thanabout 5 g./l. of the additive will be used. I prefer to use baths whichcontain about 0.01 g./l. and 0.25 g./l. in the bath.

The sulfonated alkyl diphenyl oxides are solid materials and arepreferably added to the bath in the form of an aqueous solution. Whensuch solutions are stored,

producea minimum of spray and mi stduring the electro 1 depositionofchromium. a H v It has been found that the sulfonated alkyl diphenyloxides are efiective in reducing spray and mist. in the; various typesof chromic acid baths. The se include.

baths containing sulfate catalyst, :and also those containing mixedcatalysts. It iselfective in low conceni atentecl oct. 18, 1960Illustrative metals includesodium, potassium, lithium, trivalentchromium, calcium,

The disodi tration baths, such as those containing 180 to 250 g./l. ofchromic acid, as well as medium and high concentration baths containingas much as 550 to 600 g./l. of chromic acid. These baths are operatedunder conventional process conditions. The chromium electroplating bathsreferred to herein are the conventional hexavaient chromium bathscomprised largely of chromic acid. Although these baths are commonlyreferred to as being formed from chromic acid, they are more correctlynoted as being formed from chromic anhydride or equivalent material.

For the purpose of further illustrating the advantages of the presentinvention, the following illustrative examples are included:

Chromium electrodeposition was carried out in a standard cell byelectrolysis using insoluble lead anodes and plating on the cathode.Standard conditions were used unless otherwise specified.

CrO g./l.. 250 50.; (as Na SO g./l 2.5 The sodium salt of sulfonateddodecyl diphenyl oxide g./l 0.25 Temperature F..- 110 C.D.1 a.s.i.

CrO g./l 325 S g./l 3.25 The sodium salt of sulfonated dodecyl diphenyloxide g./l 1.0 Temperature F..- 120 C.D.--1.5 a.s.i.

CrO g/l 400 S0 g./l 4.0 The sodium salt of sulfonated dodecyl diphenyloxide g./l 5.0 Temperature F..- 105 C.D.0.75 a.s.i.

CrO g./l 250 S0, g./l 2.5 The sodium salt of sulfonated dodecyl diphenyloxide g./l 0.5 Temperature F 130 C.D.2.5 a.s.i.

CrO g./l 400 K SiF In excess of saturation SrSO, In excess of saturationC.D.-1 a.s.i.

The sodium salt of sulfonated dodecyl diphenyl oxide (a) 2 g./l"Temperature, F- 110 (b) 0.25 g./l do 110 (c) 0.25 g./l dd 130 (d) 0.025g./l. do 110 (e) 0.025 g./] do- 130 010 g./l 250 K SiF In excess ofsaturation SrSO In excess of saturation Kgcl'zoq g./l 10 SrCrO g./l 5C.D.- --1 a.s.i.

The sodium salt of sulfonated dodecyl diphenyl oxide (a) 1 g./lTemperature, F-.. 130 (b) 0.25g./1 do (c) 0.25 g./l. do.. 130 (d) 0.025g./l do.. 110 (e) 0.025 g./l do 130 (f) 0.01 g./l do The additive usedin the noted tests was a mixture of the disddium salts of monododecyldiphenyl oxide disulfonate and didodecyl diphenyl oxide disulfonate (4:1ratio). The potassium salts are as effective, as are the homologousalkyl substituted compounds.

The baths made up and operated as specified in the examples haverelatively thin stable foam blankets at the surface and exhibit asubstantial reduction of the amount of mist and spray when compared tosimilar baths used as controls. Service tats illustrated that the bathswere etfective for relatively long periods of time with outreplenishment and that the baths could be maintained in excellentcondition by periodic additions of the additive. An unusual feature ofthe baths containing very small amounts of the sulfonated alkyl diphenyloxides is that they effectively operate with a minimum of spray and mistand yet, many of the baths have such a small concentration of theadditive that there is little discernable lowering of surface tension.Life tests run over relatively long periods of time did not indicate anybuildup of harmful decomposition products.

The chromium deposits produced under standard conditions were bright andmeet the usual commercial standards. The sulfonated alkyl diphenyloxides are compatible in the baths with the other usual bath componentsand additives, including other additives used as antimisting agents.Pilot plant studies of baths containing the sulfonated aikyl diphenyloxides disclose that over a period of time substantially less chromicacid had to be replaced in the bath. This is attributable to thedecrease in spray and mist, both of which contribute to large chromicacid losses in baths without an anti-misting additive. In light of theforegoing description, the following is claimed:

1. An improved bath for the electrodeposition of chromium comprising anaqueous acid chromium plating solution and as an anti-misting additive,a small amount sufiicien t to substantially decrease mist in said bathof a disulfonated alkyl diphenyl oxide.

2. An improved bath for the electrodeposition of chromium comprising anaqueous chromic acid chromium plating solution and as an anti-mistingadditive, at least 0.005 g./l. of at least one compound having thegeneral formula Rn R wherein R is an alkyl group having 6 to 18 carbonatoms, and n is an integer having a value from 0 to 1.

3. A bath as set forth in claim No. 2, containing between 0.1 g./l. and0.25 g./l. of the additive.

4. A bath as set forth in claim No. 3 in which R is selected from theclass consisting of octyl, nonyl and dodecytl.

5. A bath as set fonth in claim No. 2 in which the anti-misting additiveis added in the form, of the disod-ium salt of disulfonated monododecyldiphenyl oxide.

6. A bath as set forth in claim No. 2, in which the anti-mistingadditive is added in the form of the potassium salt of disulfonatedmonododecyl diphenyl oxide.

7. A bath as set forth in claim No. 2, in which R is an octyl group.

8. A bath as set forth in claim No. 2, in which R is a nonyl group.

1 a la cces iq s e qs sp itias ih 'Q llill l nata with a minimum ofspray and mist the improvement which comprises electroplating chromiumfrom an aqueous chromic acid bath to which has been added a small amountsufl'icient to substantially decrease mist in said bath of disulfonatedalkyl diphenyl oxide.

10. In a process for eleotrodepo-siting chromium metal with a minimum ofspray and mist the improvement which comprises electroplating chromiumfrom an aqueous chromic acid bath to which has been added at least 0.005g./l. of at least one compound having the general formula wherein R isan alkyl group having 6 to 18 carbon atoms, 11 is an integer having avalue from 0 to 1, and X is a cation selected from the class consistingof hydrogen, ammonium, and a metal.

11. A liquid anti-misting additive for minimizing the formation of mistand spray from aqueous chromic acid baths during electrolysis comprisingan aqueous solution of a disulfonated alkyl diphenyl oxide stabilized toprevent mold formation with an alkali salt of a chromic acid selectedfrom the class consisting of chromic and dichromic acids in suflicientamount to effect said stabilization.

12. A liquid anti-misting additive for minimizing the formation of mistand spray from aqueous chromic acid baths during electrolysis comprisingan aqueous solution of at least one compound having the general formulain which R is a dodecyl group, n is an integer having a value from 0 to1, and X is sodium, stabilized to prevent mold formation with an alkalimetal chromate in suflicient amount to elfect said stabilization.

14. The composition of matter of claim No. 13 in which the alkyldiphenyl oxide additive comprises a mixture of the disodium salt ofmonododecyl diphenyl oxide disulfonate and didodecyl diphenyl oxidedisulfonate in a ratio of about 4 to 1.

15. An improved bath for the electrodeposition of chromium comprising anaqueous chromic acid chromium plating solution and, as an anti-mistingadditive, a small amount sutficient to substantially decrease mist insaid bath of octadecyldiphenyl oxide sulfonate.

Brown June 12, 1956 p

2. AN IMPROVED BATH FOR THE ELECTRODEPOSITION OF CHROMIUM COMPRISING AN AQUEOUS CHROMIC ACID CHROMIUM PLATING SOLUTION AND AS AN ANTI-MISTING ADDITIVE, AT LEAST 0.005 G./L. OF AT LEAST ONE COMPOUND HAVING THE GENERAL FORMULA 